Mammography plays a vital part in the early detection of breast cancer. Unfortunately, mammography units being used today have never been analyzed from a systems point of view. Multiparameter optimization studies of a mammography system have been reported by Muntz et al (Med. Phys 12, 5, 1985) in which the patient dose has been minimized, while maintaining satisfactory image quality. The most important new feature of the design is the presence of an array of thin metal vanes arranged in an arc about the x-ray source, between the breast and the film. The vanes absorb scattered radiation and thus improve the quality of the image. In order for the vanes not to image on the film the grid must move in a precisely controlled profile during the exposure.